The present invention relates to testing of radio frequency (RF) signal transmitters designed to perform beamforming, and in particular, to detecting phase shifts of RF signals emitted from elements of an antenna array for comparison with expected signal phase differences.
Many of today's electronic devices use wireless signal technologies for both connectivity and communications purposes. Because wireless devices transmit and receive electromagnetic energy, and because two or more wireless devices have the potential of interfering with the operations of one another by virtue of their signal frequencies and power spectral densities, these devices and their wireless signal technologies must adhere to various wireless signal technology standard specifications.
When designing such wireless devices, engineers take extra care to ensure that such devices will meet or exceed each of their included wireless signal technology prescribed standard-based specifications. Furthermore, when these devices are later being manufactured in quantity, they are tested to ensure that manufacturing defects will not cause improper operation, including their adherence to the included wireless signal technology standard-based specifications.
Testing of such wireless devices typically involves testing of the receiving and transmitting subsystems of the device under test (DUT). The testing system will send a prescribed sequence of test data packet signals to a DUT, e.g., using different frequencies, power levels, and/or signal modulation techniques to determine if the DUT receiving subsystem is operating properly. Similarly, the DUT will send test data packet signals at a variety of frequencies, power levels, and/or modulation techniques for reception and processing by the testing system to determine if the DUT transmitting subsystem is operating properly.
For testing these devices following their manufacture and assembly, current wireless device test systems typically employ testing systems having various subsystems for providing test signals to each device under test (DUT) and analyzing signals received from each DUT. Some systems (often referred to as “testers”) include at least a vector signal generator (VSG) for providing the source signals to be transmitted to the DUT, and a vector signal analyzer (VSA) for analyzing signals produced by the DUT. The production of test signals by the VSG and signal analysis performed by the VSA are generally programmable (e.g., through use of an internal programmable controller or an external programmable controller such as a personal computer) so as to allow each to be used for testing a variety of devices for adherence to a variety of wireless signal technology standards with differing frequency ranges, bandwidths and signal modulation characteristics.
Wireless devices, such as cellphones, smartphones, tablets, etc., make use of standards-based technologies, such as IEEE 802.11a/b/g/n/ac/ad (“Wi-Fi”), 3GPP LTE, and Bluetooth. The standards that underlie these technologies are designed to provide reliable wireless connectivity and/or communications. The standards prescribe physical and higher-level specifications generally designed to be energy-efficient and to minimize interference among devices using the same or other technologies that are adjacent to or share the wireless spectrum.
Tests prescribed by these standards are meant to ensure that such devices are designed to conform to the standard-prescribed specifications, and that manufactured devices continue to conform to those prescribed specifications. Most devices are transceivers, containing at least one or more receivers and transmitters. Thus, the tests are intended to confirm whether the receivers and transmitters both conform. Tests of the receiver or receivers (RX tests) of a DUT typically involve a test system (tester) sending test packets to the receiver(s) and some way of determining how the DUT receiver(s) respond to those test packets. Transmitters of a DUT are tested by having them send packets to the test system, which then evaluates the physical characteristics of the signals sent by the DUT.
More particularly, the IEEE 802.11ad standard provides specifications for wireless communications using millimeter wave frequencies centered nominally about 60 GHz. At those frequencies, signal attenuation is quite pronounced relative to lower-frequency Wi-Fi standards, such as 802.11n. Thus, omni-directional signal radiation is problematic. Instead, devices that subscribe to IEEE 802.11ad generally employ beamforming to obtain directional signal gain. Two devices establishing an 802.11ad link are designed to work cooperatively to determine a signal path producing an optimal signal-to-noise ratio (SNR) prior to sending data packets containing payload data. At least one of such two devices will have the ability to beamform to achieve that optimal signal path. A common way of achieving this is for the beamforming device to use an antenna array in which each antenna element can have its transmitted signal phase shifted in predetermined increments (e.g., of 90 degrees thereby producing four distinct phases, or 11.25 degrees thereby producing 32 distinct phases). When antenna elements emit their transmit signals at particular phase shifts, this changes how the signal radiating from that element will interact with signals radiating from other elements. In essence, where these signals meet in space, they will undergo constructive (additive) or destructive (subtractive) interference. The resulting aggregation of such instances of interference determines the net signal gain realized from one device to the other. By appropriate adjustment of such phase shifts, an optimal effective SNR can be achieved between the two devices.
During manufacturing, a device designed for controlled shifting of signal phases that drive an integral or external antenna array, may experience a manufacturing defect that negatively affects in part or completely the ability of the device to shift phases and to beamform. Hence, during manufacturing test, sufficient testing may determine whether a device is properly shifting phases of the signals driving and being radiated from the antenna array elements, as well as whether the resulting effective radiated signal power stays within the applicable specification.
However, testing each device for each phase shift on each antenna element typically requires a relatively significant amount of test time. Therefore, it would be desirable to have a technique that reduces start and stop control and supports a continuous signal flow as phase shift adjustments were made along with the detection of phase-shift instances and captures of signal characteristics before and after such phase changes. This would decrease required test times and result in commensurately lower testing costs.